javax.microedition.lcdui
Class Graphics

Drawing primitives are provided for text, images, lines, rectangles,
and arcs. Rectangles and arcs may also be filled with a solid color.
Rectangles may also be specified with rounded corners.

The only drawing operation provided is pixel replacement. The
destination pixel value is simply replaced by the current
pixel value specified in the graphics object being used for
rendering. No facility for combining pixel values, such as
raster-ops or alpha blending, is provided.

A 24-bit color model is provided, with 8 bits for each of red, green, and
blue components of a color. Not all devices support a full 24 bits' worth
of color and thus they will map colors requested by the application into
colors available on the device. Facilities are provided in the Display class for obtaining device characteristics, such as
whether color is available and how many distinct gray levels are available.
This enables applications to adapt their behavior to a device without
compromising device independence.

For all rendering operations, source pixels are always
combined with destination pixels using the Source Over
Destination rule [Porter-Duff]. Other schemes for
combining source pixels with destination pixels, such
as raster-ops, are not provided.

For the text, line, rectangle, and arc drawing and
filling primitives, the source pixel is a pixel
representing the current color of the graphics object
being used for rendering. This pixel is always considered
to be fully opaque. With source pixel that is always
fully opaque, the Source Over Destination rule has the
effect of pixel replacement, where destination pixels are
simply replaced with the source pixel from the graphics object.

The drawImage() and drawRegion() methods use an image as the source
for rendering operations instead of the current color of the
graphics object. In this context, the Source Over Destination
rule has the following properties: a fully opaque pixel in
the source must replace the destination pixel, a fully
transparent pixel in the source must leave the destination
pixel unchanged, and a semitransparent pixel in the source
must be alpha blended with the destination pixel. Alpha
blending of semitransparent pixels is required. If an implementation
does not support alpha blending, it must remove all
semitransparency from image source data at the time the image
is created. See Alpha Processing for further discussion.

The destinations of all graphics rendering are considered to consist
entirely of fully opaque pixels. A property of the Source Over
Destination rule is that compositing any pixel with a fully
opaque destination pixel always results in a fully opaque destination
pixel. This has the effect of confining full and partial transparency
to immutable images, which may only be used as the source for rendering operations.

Graphics may be rendered directly to the display or to an off-screen
image buffer. The destination of rendered graphics depends on the
provenance of the graphics object. A graphics object for rendering
to the display is passed to the Canvas object's
paint()
method. This is the only means by which a graphics object may
be obtained whose destination is the display. Furthermore, applications
may draw using this graphics object only for the duration of the
paint() method.

A graphics object for rendering to an off-screen image buffer may
be obtained by calling the
getGraphics()
method on the desired image.
A graphics object so obtained may be held indefinitely
by the application, and requests may be issued on this graphics
object at any time.

The default coordinate system's origin is at the
upper left-hand corner of the destination. The X-axis direction is
positive towards the right, and the Y-axis direction is positive
downwards. Applications may assume that horizontal and vertical
distances in the coordinate system represent equal distances on the
actual device display, that is, pixels are square. A facility is provided
for translating the origin of the coordinate system.
All coordinates are specified as integers.

The coordinate system represents locations between pixels, not the
pixels themselves. Therefore, the first pixel in the upper left corner
of the display lies in the square bounded by coordinates
(0,0) , (1,0) , (0,1) , (1,1).

Under this definition, the semantics for fill operations are clear.
Since coordinate grid lines lie between pixels, fill operations
affect pixels that lie entirely within the region bounded by the
coordinates of the operation. For example, the operation

g.fillRect(0, 0, 3, 2)

paints exactly six pixels. (In this example, and in all subsequent
examples, the variable g is assumed to contain a reference to a
Graphics object.)

Each character of a font contains a set of pixels that forms the shape of
the character. When a character is painted, the pixels forming the
character's shape are filled with the Graphics object's current color, and
the pixels not part of the character's shape are left untouched.
The text drawing calls
drawChar(),
drawChars(),
drawString(), and
drawSubstring()
all draw text in this manner.

Lines, arcs, rectangles, and rounded rectangles may be drawn with either a
SOLID or a DOTTED stroke style, as set by the setStrokeStyle() method. The stroke style does not affect fill, text, and
image operations.

For the SOLID stroke style,
drawing operations are performed with a one-pixel wide pen that fills
the pixel immediately
below and to the right of the specified coordinate. Drawn lines
touch pixels at both endpoints. Thus, the operation

g.drawLine(0, 0, 0, 0)

paints exactly one pixel, the first pixel in the upper left corner
of the display.

Drawing operations under the DOTTED stroke style will touch a subset of
pixels that would have been touched under the SOLID stroke style. The
frequency and length of dots is implementation-dependent. The endpoints of
lines and arcs are not guaranteed to be drawn, nor are the corner points of
rectangles guaranteed to be drawn. Dots are drawn by painting with the
current color; spaces between dots are left untouched.

An artifact of the coordinate system is that the area affected by a fill
operation differs slightly from the area affected by a draw operation given
the same coordinates. For example, consider the operations

g.fillRect(x, y, w, h); // 1
g.drawRect(x, y, w, h); // 2

Statement (1) fills a rectangle w pixels wide and h pixels high.
Statement (2) draws a rectangle whose left and top
edges are within the area filled by statement (1). However, the
bottom and right edges lie one pixel outside the filled area.
This is counterintuitive, but it preserves the invariant that

The exact pixels painted by drawLine() and drawArc() are not
specified. Pixels touched by a fill operation must either
exactly overlap or directly abut pixels touched by the
corresponding draw operation. A fill operation must never leave
a gap between the filled area and the pixels touched by the
corresponding draw operation, nor may the fill operation touch
pixels outside the area bounded by the corresponding draw operation.

Clipping

The clip is the set of pixels in the destination of the Graphics
object that may be modified by graphics rendering operations.

There is a single clip per Graphics object. The only pixels
modified by graphics operations are those that lie within
the clip. Pixels outside the clip are not modified by
any graphics operations.

Operations are provided for intersecting the current clip
with a given rectangle and for setting the current clip
outright. The application may specify the clip by supplying
a clip rectangle using coordinates relative to the current
coordinate system.

It is legal to specify a clip rectangle whose width or height
is zero or negative. In this case the clip is considered to
be empty, that is, no pixels are contained within it. Therefore,
if any graphics operations are issued under such a clip, no
pixels will be modified.

It is legal to specify a clip rectangle that extends
beyond or resides entirely beyond the bounds of the
destination. No pixels exist outside the bounds of the
destination, and the area of the clip rectangle that is
outside the destination is ignored. Only the pixels that
lie both within the destination and within the specified
clip rectangle are considered to be part of the clip.

Operations on the coordinate system, such as translate(),
do not modify the clip. The methods getClipX(), getClipY(),
getClipWidth() and getClipHeight() must return a rectangle
that, if passed to setClip without an intervening change to
the Graphics object's coordinate system, must result in the
identical set of pixels in the clip. The rectangle returned
from the getClip family of methods may differ from the clip
rectangle that was requested in setClip(). This can occur if
the coordinate system has been changed or if the implementation
has chosen to intersect the clip rectangle with the bounds of
the destination of the Graphics object.

If a graphics operation is affected by the clip rectangle, the pixels
touched by that operation must be the same ones that would be touched
as if the clip rectangle did not affect the operation. For example,
consider a clip rectangle (cx, cy, cw, ch) and a point (x1, y1) that
lies outside this rectangle and a point (x2, y2) that lies within this
rectangle. In the following code fragment,

The pixels touched by statement (4) must be identical to the pixels
within (cx, cy, cw, ch) touched by statement (3).

Anchor Points

The drawing of text is based on "anchor points".
Anchor points are used to minimize the amount of
computation required when placing text.
For example, in order to center a piece of text,
an application needs to call stringWidth() or
charWidth() to get the width and then perform a
combination of subtraction and division to
compute the proper location.
The method to draw text is defined as follows:

public void drawString(String text, int x, int y, int anchor);

This method draws text in the current color,
using the current font
with its anchor point at (x,y). The definition
of the anchor point must be one of the
horizontal constants (LEFT, HCENTER, RIGHT)
combined with one of the vertical constants
(TOP, BASELINE, BOTTOM) using the logical OR operator.

Vertical centering of the text is not specified since it is not considered
useful, it is hard to specify, and it is burdensome to implement. Thus,
the VCENTER value is not allowed in the anchor point parameter of text
drawing calls.

The actual position of the bounding box
of the text relative to the (x, y) location is
determined by the anchor point. These anchor
points occur at named locations along the
outer edge of the bounding box. Thus, if f
is g's current font (as returned by
g.getFont(), the following calls will all have
identical results:

For text drawing, the inter-character and inter-line spacing (leading)
specified by the font designer are included as part of the values returned
in the stringWidth() and getHeight()
calls of class Font.
For example, given the following code:

draws string1 and string2 on separate lines with
an appropriate amount of inter-line spacing.

The stringWidth() of the string and the fontHeight() of the font in which
it is drawn define the size of the bounding box of a piece of text. As
described above, this box includes inter-line and inter-character spacing.
The implementation is required to put this space below and to right of the
pixels actually belonging to the characters drawn. Applications that wish
to position graphics closely with respect text (for example, to paint a
rectangle around a string of text) may assume that there is space below and
to the right of a string and that there is no space above and to the
left of the string.

Anchor points are also used for positioning of images. Similar to text
drawing, the anchor point for an image specifies the point on the bounding
rectangle of the destination that is to positioned at the (x,y) location
given in the graphics request. Unlike text, vertical centering of images
is well-defined, and thus the VCENTER value may be used within the anchor
point parameter of image drawing requests. Because images have no notion
of a baseline, the BASELINE value may not be used within the anchor point
parameter of image drawing requests.

DOTTED

translate

public void translate(int x,
int y)

Translates the origin of the graphics context to the point
(x, y) in the current coordinate system. All coordinates
used in subsequent rendering operations on this graphics
context will be relative to this new origin.

The effect of calls to translate() are cumulative. For example, calling
translate(1, 2) and then translate(3, 4) results in a translation of
(4, 6).

The application can set an absolute origin (ax, ay) using the following
technique:

getBlueComponent

getGrayScale

public int getGrayScale()

Gets the current grayscale value of the color being used for rendering
operations. If the color was set by setGrayScale(), that value is simply
returned. If the color was set by one of the methods that allows setting
of the red, green, and blue components, the value returned is computed from
the RGB color components (possibly in a device-specific fashion) that best
approximates the brightness of that color.

Returns:

integer value in range 0-255

setColor

public void setColor(int red,
int green,
int blue)

Sets the current color to the specified RGB values. All subsequent
rendering operations will use this specified color.

setColor

public void setColor(int RGB)

Sets the current color to the specified RGB values. All subsequent
rendering operations will use this specified color. The RGB value
passed in is interpreted with the least significant eight bits
giving the blue component, the next eight more significant bits
giving the green component, and the next eight more significant
bits giving the red component. That is to say, the color component
is specified in the form of 0x00RRGGBB. The high order byte of this value
is ignored.

Parameters:

RGB - the color being set

setGrayScale

public void setGrayScale(int value)

Sets the current grayscale to be used for all subsequent
rendering operations. For monochrome displays, the behavior
is clear. For color displays, this sets the color for all
subsequent drawing operations to be a gray color equivalent
to the value passed in. The value must be in the range 0-255.

getClipX

public int getClipX()

Gets the X offset of the current clipping area, relative
to the coordinate system origin of this graphics context.
Separating the getClip operation into two methods returning
integers is more performance and memory efficient than one
getClip() call returning an object.

getClipY

public int getClipY()

Gets the Y offset of the current clipping area, relative
to the coordinate system origin of this graphics context.
Separating the getClip operation into two methods returning
integers is more performance and memory efficient than one
getClip() call returning an object.

getClipHeight

clipRect

public void clipRect(int x,
int y,
int width,
int height)

Intersects the current clip with the specified rectangle.
The resulting clipping area is the intersection of the current
clipping area and the specified rectangle.
This method can only be used to make the current clip smaller.
To set the current clip larger, use the setClip method.
Rendering operations have no effect outside of the clipping area.

drawRect

public void drawRect(int x,
int y,
int width,
int height)

Draws the outline of the specified rectangle using the current
color and stroke style.
The resulting rectangle will cover an area (width + 1)
pixels wide by (height + 1) pixels tall.
If either width or height is less than
zero, nothing is drawn.

drawRoundRect

Draws the outline of the specified rounded corner rectangle
using the current color and stroke style.
The resulting rectangle will cover an area (width + 1) pixels wide
by (height + 1) pixels tall.
If either width or height is less than
zero, nothing is drawn.

fillArc

The resulting arc begins at startAngle and extends
for arcAngle degrees.
Angles are interpreted such that 0 degrees
is at the 3 o'clock position.
A positive value indicates a counter-clockwise rotation
while a negative value indicates a clockwise rotation.

The center of the arc is the center of the rectangle whose origin
is (x, y) and whose size is specified by the
width and height arguments.

If either width or height is zero or less,
nothing is drawn.

The filled region consists of the "pie wedge" region bounded by the arc
segment as if drawn by drawArc(), the radius extending from the center to
this arc at startAngle degrees, and radius extending from the
center to this arc at startAngle + arcAngle degrees.

The angles are specified relative to the non-square extents of
the bounding rectangle such that 45 degrees always falls on the
line from the center of the ellipse to the upper right corner of
the bounding rectangle. As a result, if the bounding rectangle is
noticeably longer in one axis than the other, the angles to the
start and end of the arc segment will be skewed farther along the
longer axis of the bounds.

Parameters:

x - the x coordinate of the upper-left corner of
the arc to be filled.

y - the y coordinate of the upper-left corner of the
arc to be filled.

width - the width of the arc to be filled

height - the height of the arc to be filled

startAngle - the beginning angle.

arcAngle - the angular extent of the arc,
relative to the start angle.

drawArc

Draws the outline of a circular or elliptical arc
covering the specified rectangle,
using the current color and stroke style.

The resulting arc begins at startAngle and extends
for arcAngle degrees, using the current color.
Angles are interpreted such that 0 degrees
is at the 3 o'clock position.
A positive value indicates a counter-clockwise rotation
while a negative value indicates a clockwise rotation.

The center of the arc is the center of the rectangle whose origin
is (x, y) and whose size is specified by the
width and height arguments.

The resulting arc covers an area
width + 1 pixels wide
by height + 1 pixels tall.
If either width or height is less than zero,
nothing is drawn.

The angles are specified relative to the non-square extents of
the bounding rectangle such that 45 degrees always falls on the
line from the center of the ellipse to the upper right corner of
the bounding rectangle. As a result, if the bounding rectangle is
noticeably longer in one axis than the other, the angles to the
start and end of the arc segment will be skewed farther along the
longer axis of the bounds.

Parameters:

x - the x coordinate of the upper-left corner of the arc to be drawn.

y - the y coordinate of the upper-left corner of the arc to be drawn.

width - the width of the arc to be drawn

height - the height of the arc to be drawn

startAngle - the beginning angle

arcAngle - the angular extent of the arc, relative to the start angle.

drawRegion

Copies a region of the specified source image to a location within
the destination, possibly transforming (rotating and reflecting)
the image data using the chosen transform function.

The destination, if it is an image, must not be the same image as
the source image. If it is, an exception is thrown. This restriction
is present in order to avoid ill-defined behaviors that might occur if
overlapped, transformed copies were permitted.

The transform function used must be one of the following, as defined
in the Sprite class:Sprite.TRANS_NONE - causes the specified image
region to be copied unchangedSprite.TRANS_ROT90 - causes the specified image
region to be rotated clockwise by 90 degrees.Sprite.TRANS_ROT180 - causes the specified image
region to be rotated clockwise by 180 degrees.Sprite.TRANS_ROT270 - causes the specified image
region to be rotated clockwise by 270 degrees.Sprite.TRANS_MIRROR - causes the specified image
region to be reflected about its vertical center.Sprite.TRANS_MIRROR_ROT90 - causes the specified image
region to be reflected about its vertical center and then rotated
clockwise by 90 degrees.Sprite.TRANS_MIRROR_ROT180 - causes the specified image
region to be reflected about its vertical center and then rotated
clockwise by 180 degrees.Sprite.TRANS_MIRROR_ROT270 - causes the specified image
region to be reflected about its vertical center and then rotated
clockwise by 270 degrees.

If the source region contains transparent pixels, the corresponding
pixels in the destination region must be left untouched. If the source
region contains partially transparent pixels, a compositing operation
must be performed with the destination pixels, leaving all pixels of
the destination region fully opaque.

The (x_src, y_src) coordinates are relative to
the upper left
corner of the source image. The x_src,
y_src, width, and height
parameters specify a rectangular region of the source image. It is
illegal for this region to extend beyond the bounds of the source
image. This requires that:

The (x_dest, y_dest) coordinates are relative to
the coordinate
system of this Graphics object. It is legal for the destination
area to extend beyond the bounds of the Graphics
object. Pixels
outside of the bounds of the Graphics object will
not be drawn.

The transform is applied to the image data from the region of the
source image, and the result is rendered with its anchor point
positioned at location (x_dest, y_dest) in the
destination.

Parameters:

src - the source image to copy from

x_src - the x coordinate of the upper left corner of the region
within the source image to copy

y_src - the y coordinate of the upper left corner of the region
within the source image to copy

width - the width of the region to copy

height - the height of the region to copy

transform - the desired transformation for the selected region
being copied

x_dest - the x coordinate of the anchor point in the
destination drawing area

y_dest - the y coordinate of the anchor point in the
destination drawing area

anchor - the anchor point for positioning the region within
the destination image

copyArea

Copies the contents of a rectangular area
(x_src, y_src, width, height) to a destination area,
whose anchor point identified by anchor is located at
(x_dest, y_dest). The effect must be that the
destination area
contains an exact copy of the contents of the source area
immediately prior to the invocation of this method. This result must
occur even if the source and destination areas overlap.

The points (x_src, y_src) and (x_dest,
y_dest) are both specified
relative to the coordinate system of the Graphics
object. It is
illegal for the source region to extend beyond the bounds of the
graphic object. This requires that:

where tx and ty represent the X and Y
coordinates of the translated origin of this graphics object, as
returned by getTranslateX() and
getTranslateY(), respectively.

However, it is legal for the destination area to extend beyond
the bounds of the Graphics object. Pixels outside
of the bounds of
the Graphics object will not be drawn.

The copyArea method is allowed on all
Graphics objects except those
whose destination is the actual display device. This restriction is
necessary because allowing a copyArea method on
the display would
adversely impact certain techniques for implementing
double-buffering.

Like other graphics operations, the copyArea
method uses the Source
Over Destination rule for combining pixels. However, since it is
defined only for mutable images, which can contain only fully opaque
pixels, this is effectively the same as pixel replacement.

Parameters:

x_src - the x coordinate of upper left corner of source area

y_src - the y coordinate of upper left corner of source area

width - the width of the source area

height - the height of the source area

x_dest - the x coordinate of the destination anchor point

y_dest - the y coordinate of the destination anchor point

anchor - the anchor point for positioning the region within
the destination image

drawRGB

Renders a series of device-independent RGB+transparency values in a
specified region. The values are stored in
rgbData in a format
with 24 bits of RGB and an eight-bit alpha value
(0xAARRGGBB),
with the first value stored at the specified offset. The
scanlength
specifies the relative offset within the array between the
corresponding pixels of consecutive rows. Any value for
scanlength is acceptable (even negative values)
provided that all resulting references are within the
bounds of the rgbData array. The ARGB data is
rasterized horizontally from left to right within each row.
The ARGB values are
rendered in the region specified by x,
y, width and height, and
the operation is subject to the current clip region
and translation for this Graphics object.

Consider P(a,b) to be the value of the pixel
located at column a and row b of the
Image, where rows and columns are numbered downward from the
top starting at zero, and columns are numbered rightward from
the left starting at zero. This operation can then be defined
as:

P(a, b) = rgbData[offset + (a - x) + (b - y) * scanlength]

for

x <= a < x + width
y <= b < y + height

This capability is provided in the Graphics
class so that it can be
used to render both to the screen and to offscreen
Image objects. The
ability to retrieve ARGB values is provided by the Image.getRGB(int[], int, int, int, int, int, int)
method.

If processAlpha is true, the
high-order byte of the ARGB format
specifies opacity; that is, 0x00RRGGBB specifies a
fully transparent
pixel and 0xFFRRGGBB specifies a fully opaque
pixel. Intermediate
alpha values specify semitransparency. If the implementation does not
support alpha blending for image rendering operations, it must remove
any semitransparency from the source data prior to performing any
rendering. (See Alpha Processing for
further discussion.)
If processAlpha is false, the alpha
values are ignored and all pixels
must be treated as completely opaque.

The mapping from ARGB values to the device-dependent
pixels is platform-specific and may require significant
computation.

Parameters:

rgbData - an array of ARGB values in the format
0xAARRGGBB

offset - the array index of the first ARGB value

scanlength - the relative array offset between the
corresponding pixels in consecutive rows in the
rgbData array

x - the horizontal location of the region to be rendered

y - the vertical location of the region to be rendered

width - the width of the region to be rendered

height - the height of the region to be rendered

processAlpha - true if rgbData
has an alpha channel,
false if all pixels are fully opaque

Throws:

ArrayIndexOutOfBoundsException - if the requested operation
will attempt to access an element of rgbData
whose index is either negative or beyond its length

getDisplayColor

public int getDisplayColor(int color)

Gets the color that will be displayed if the specified color
is requested. This method enables the developer to check the
manner in which RGB values are mapped to the set of distinct
colors that the device can actually display. For example,
with a monochrome device, this method will return either
0xFFFFFF (white) or 0x000000 (black)
depending on the brightness of the specified color.